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The little fish have been an economic and nutritional mainstay for some 10 million people in neighboring Burundi, Tanzania, Zambia and the Democratic Republic of Congo — four of the poorest countries on Earth. They also depend on Lake Tanganyika for drinking water.

But that could change, according to research published in the online version of the journal Nature Geoscience. Using samples of the lakebed that chart a 1,500-year history of the lake’s surface water temperature, the scientists found the current temperature — 78.8 degrees F (26 degrees C) — is the warmest it’s been in a millennium and a half. And that could play havoc with sardines and other fish the local people depend on.

The scientists also found that the lake saw its biggest warm-up in the 20th century.

This unprecedented warm water could interfere with the lake’s unique ecosystem, which relies on nutrients churned up from the bottom of the lake to feed the algae that form the base of the lake’s food web. As Lake Tanganyika heats up, the mixing of waters is lessened and fewer nutrients get to the top level where algae and fish feed. More warming at the surface magnifies the difference between the two lake levels and even more wind is needed to churn the waters enough to get nutrients to the upper layer.

Some researchers believe declining fish stocks in Lake Tanganyika are due mainly to overfishing. However, climate change models show a general warming trend in the region, which would cause even greater warming of Lake Tanganyika’s surface. But in a statement from the U.S. National Science Foundation, which helped fund the research, scientists said that warming of the lake is making the decline in fish stocks worse, even if that is not the cause.

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I started with Reuters in 1986 in New York City, moving to Washington DC two years later. I've covered the Winter Olympics in Calgary and Salt Lake City, a couple wars, the State Department, White House, Pentagon, several long trials and a presidential sex scandal. Since 2006, I've been reporting on the environment and climate change.